The present exemplary embodiment relates generally to fusing of images in a printing system including a plurality of marking engines. It finds particular application in conjunction with a printing system which includes first and second tandem marking engines where the second marking engine receives print media which has been preheated by the fuser of the first marking engine, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
In a typical xerographic marking engine, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto the paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure.
The reliability of fusers, and in particular, fusers for color marking engines, tends to be low when compared with the other components of a printing machine. This is primarily due to high temperatures and material strains and stresses employed in forming a long dwell time in the nip. To achieve a high gloss at reasonable temperatures in color applications, the surface smoothness (Ra) is generally about 0.4 microns or less. Over time, the color fuser roll tends to wear, resulting in non-uniformities in the surface of the roll, which, in turn, lead to gloss non-uniformities. Additionally, the lifetime of the fuser roll material is limited by the desire to provide compressibility to achieve an adequate nip width, which affects the dwell time for heating, and provide sufficient differential speeds to enable stripping and release.
Systems which incorporate several marking engines have been developed. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple printers. Such systems are commonly referred to as “tandem engine” printers, “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different printers, such as separate printing of the color and monochrome pages). In some systems, a process known as “tandem duplex printing” is employed. In this process, a first marking engine applies an image to a first side of a sheet and a second marking engine applies an image to a second side of the sheet. Each of the marking engines is thus operating in a simplex mode to generate a duplex print. This has been found to be more efficient for some applications than using a single marking engine with an internal duplex path to create a duplex print.
Such integrated printing systems have multiple fusers since each marking engine incorporates the fuser or fusers appropriate for fusing the images applied by that particular marking engine. As a result, the reliability of the individual fusers has a significant impact on overall reliability, since any one fuser failure can affect the productivity of the entire system.